Reed relay trigger circuit



Feb. 18, 1964 B. H. ARNOLD 3,121,827

REED RELAY TRIGGER CIRCUIT Filed Oct. 26. 1961 we: 3" SOURCE I 32 as I 2e a ifi 1o |u u oJL F {FNMA D\ 21 A M 21 C v K13 15 14 \H 2 I V PU 2 E 23 B 53 OUT T i zs 24 $19 20 18 voLA o uRcE B- I FIG.1

VOLTAGE 'RELAY10ENERGIZED RELAY 11 ENERGIZED' RELAY 1i DENERGIZED RELAY 10 DENERGIZED AT INPUT T0 28 II 29 L l AT D 1 i 12,E 1 p i 5 E AT A i l E 5 I l k 6 %:1 Y 1 i '+I- Q 187- 5 E i L I ATB I i 5 V I l -30I I +12:' i AT OUTPUT 3o I l D l I I I l T1 T2 T3 T4 T5 T6 TIME INVENTOR BRUCE H. ARN 0 FIG. 2 BY Q4 6% ATTORNEY United States Patent 3,121,827 REED RELAY TRIGGER ClRCUlT Bruce H. Arnold, Whitney Point, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Oct. 26, 1961, Ser. No. 147,927 7 Claims. (Cl. 317-140) This invention relates to trigger circuits, and more particularly to those alternately operable to one or the other of two stable states by successive pulses from a single source.

Reed relays are relatively simple switching devices which are less expensive than vacuum tubes and transistors and respond faster than conventional wire contact relays. Although reed relays have been proposed comprising a movable reed or armature adapted to selectively contact a normally open reed contact point or a normally closed reed contact point, reed relays of this transfer type have never been manufactured successfully on a commercial basis. The only type of reed relay in widespread use comprises an armature reed which upon energization of a coil is adapted to make contact with a normally open reed contact point.

Trigger circuits are known which employ two conventional wire contact relays that are alternately energized in response to successive pulses from a single source. The coil of each such conventional relay is cross-coupled through a normally closed contact point of the other con ventional relay such that energization of one of the relays will effect drop out of the remaining relay. However, since the reed relays currently commercially available are equivalent to conventional relays with a single normally open point, it will be apparent that a reed relay trigger circuit cannot be evolved merely by substituting reed relays for conventional wire contact relays.

The principal object of this invention is therefore to provide a trigger circuit which is less expensive than those embodying transistors, vacuum tubes or conventional wire Ncontact relays, and yet is faster acting than those embodying conventional wire contact relays.

Another object is to provide a trigger circuit in which it is possible to employ reed relays having but a single normally open contact, thereby to take advantage of the low cost and fast operating times of reed relays.

According to these objects, the trigger circuit embodying the invention comprises two relays having only normally open contacts. A source of electrical power supplies, across the coil of one of the relays, a bias voltage insufficient to pick but suflicient to hold such relay. An input which supplies trigger pulses is coupled via the normally open contact of the second relay and one capacitor to one end of said coil, and via another capacitor of smaller capacitance to the other end of said coil. The coil of said second relay and also the normally open contact of said one relay are connected in parallel to said source and to an output. A latch back resistor connects the output with a point intermediate said one capacitor and the normally open contact of said second relay for reasons hereinafter explained.

When the circuit is initially connected to the source, said second relay will always be picked first, and said one relay will be de-energized. Upon the first positive input pulse, current will be supplied in parallel through both capacitors to opposite ends of the coil of said one relay. Due to differences in decay rates of the capacitors, sufiicient additional voltage above the bias voltage will be developed across the latter coil to pick said one relay for shunting the second relay coil and maintaining the output connected to said source even after the pulse ends. With said second relay dropped, the one (larger) capacitor will be cut off from the input. The next positive pulse will send current only through the smaller capacitor, thus dropping said one relay by reversing the current flow through its coil. When said one relay drops, it will open the shunt circuit around the coil of said second relay, thus causing the latter to be picked. This will return the circuit to the same condition as when initially connected to the source.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings, wherein:

FIG. 1 is a schematic view of a trigger circuit embodying the invention; and

FIG. 2 is a composite timing diagram showing changes in voltage at various times and points in the trigger circuit.

The trigger circuit embodying the invention comprises two relays 1t), 11 of the glass-encapsulated reed type. Relay it) has two overlying reeds providing a normally open contact 12, and also has a coil 13 that is wrapped around the reeds. Similarly, relay 11 has two overlying reeds providing a normally open contact 14, and a coil 15 that encircles said reeds. At least one of the reeds of each set is movable into contact with the other reed of that set upon energization of the respective coil 13 or 15 so that circuits hereinafter described may be completed through normally open contact 12 or 14, respectively.

One end of coil 13 is connected through a junction A and a resistor 16 to a source 17 of positive voltage. The opposite end of coil 13 is connected to a source 18 of nega tive voltage through a junction B and a resistor 19 of lower resistivity than resistor 16. The difference in resistivity of the resistors 16 and 19 is such as to provide across coil 13 a bias voltage which is insufficient to en ergize or pick the relay 10 but is sufiicient to hold it energized if it is picked.

One end of coil 15 is connected to the positive voltage source 17. The other end of coil 15 is connected to negative voltage source 18 through a junction C and a resistor 20.

A capacitor 21 has one side connected to junction A and the other side connected to a junction D. Junction D is connected to one of the reeds of the normally open contact 14 of relay 11. A latch back resistor 22 is interposed between and electrically connected to the junctions C and D.

A capacitor 23, which is of lesser capacitance than capacitor 21, has its respective sides connected to junction B and a junction E. A resistor 24 has its ends connected to junction E and to the negative voltage source 18. A resistor 25 has one end connected to source 18 and the other connected via a junction F to the other reed of the normally open contact 14 of relay 11. Resistors 24,

. 25 establish the normal potentials for capacitors 21, 23,

respectively, and also provide discharge paths for these capacitors.

Means, shown illustratively as a switch 26, is provided to supply positive voltage pulse signals from an input 27 to junctions E and F concurrently in parallel via diodes :3 C. Diode 31 is provided to prevent inductive kickback from the relay coils 13, 15 from driving the output voltage signal below ground level.

Assume, for sake of illustration, that the voltages provided by positive voltage source 17 and negative voltage source 18 are +12 volts and --12 volts, respectively; that the resistors 19 and 20 and also relay coils 13 and 15 each have a resistivity of 1500 ohms; that the resistivity of resistors 16, 22, 24 and 25 is 3000 ohms, 15,000 ohms, 1000 ohms and 500 ohms, respectively; and that the capacitance of capacitors 21 and 23 is 2 microtarads and .5 microf-arad, respectively.

Assume now that the various components are conditioned as shown in FIG. 1, except that the circuit is not connected to sources 17, 18 of positive and negative voltage, respectively. If, while switch 26 remains open, the circuit is connected to sources 17, 18, the voltage at junction A will be substantially 0 volts because the resistivity of resistor 16 equals the combined resistivity of coil 13 land resistor 19; and the voltage at junction B will be 6 volts. Thus, the voltage across coil 13 will be 6 volts which is insufficient to pick relay 10, although it is sufiicient [to maintain the relay energized after it has been picked.

Meanwhile, junction C is at 0 volts because it is between coil 15 and resistor 20 which are of equal resistivity. Thus, the voltage across coil 15 of relay 11 will be 12 volts because one end of the coil is connected to source 17 land the other end is connected to junction C Which is at 0 volts. Hence, relay 11 will be energized and cause closure of normally open contact 14.

Meanwhile, junction D is connected through resistor 22 to junction C, which is at 0 volts, and is also connected through closed contact 14, junction F and resistor 25 to negative source 18. Hence, the voltage at D is approximately 12 volts; and thus capacitor 21 will be charged to approximately 12 volts because its junction A side is at 0 volts. Similarly, the capacitor 23 will be charged to 6 volts, because its junction E side and junction B side are at -12 volts and 6 volts, respectively.

Thus, the voltages at various points in the circuit will be as indicated at time T1 in FIG. 2. l

Assume now that at time T2 (:FIG. 2), switch 26 is closed. Since contact 14 is closed, a positive pulse will be supplied from input 27 in parallel via diodes 29, 28 to the capacitors 21, 23, respectively. Immediately the voltage at junction D will rise temporarily from approximately 12 volts to substantially +12 volts, causing the voltage at junction A to rise from 0 volts to substantially 24 volts; and the voltage at junction 13 will rise temporarily 24 volts from 6 volts to substantially +18 volts. Since the capacitor 23 is of lesser capacitance than capacitor 21, the voltage at junction B will decay from 18 volts to 6 volts at a substantially faster rate (than the voltage at junction A will decay firorn 24 volts to 0 volts. Thus, the differential across coil 13 will increase above the 6- volt bias to a degree, and for a length of time, which is at least sufiicient to pick relay 10. As soon as relay picks, normally open contact 12 will close and thus connect junction C to the positive voltage source 17. Thus, both ends of coil will be effectively shunted by connection to source 17. Hence, relay 11 will drop and open contact 14.

Meanwhile, since junction C is connected to output 30, the output voltage will rise to 12 volts. The output voltage will remain at that value as long as relay 10 remains energized and keeps source 17 connected to output 30. Also, with relay 10 energized and 12 volts at junction C, the potential at junction D- and capacitor 21 will be held at 12 volts because, with contact 14 of relay 11 open, no current will be flowing through resistor 22.

When the positive pulse ends at time T3, such as by the opening of switch 26, the capacitor 23 will discharge through a path leading to the negative voltage source 18 through resistor 24. It is to be noted that since normally open point 14 of relay 1111s then open, the capacitor 21 cannot discharge through resistor 25; and capacitor 21 will thus remain charged to 12 volts. Meanwhile, when the pulse ends, the voltage at junction B will drop from +12 volts to 12 volts and remain there. This, in turn, will cause the voltage at junction B to drop temporarily to 30 volts and then decay back to 6 volts, and also cause the voltage at junction A to, temporarily drop to about 6 volts and then decay back to 0 volts.

As above noted, the voltage signal level at output 30 will remain at 12 volts as long as relay 10 is energized, and irrespective of when the input pulse ends. Relay 10 is deenergized by closing switch 26 at time T4 (FIG. 2). Since contact 14 is now open, this second positive pulse from input 27 will be transmitted solely through diode 28 and capacitor 23 and coil 13 to junction A. Latch back resistor 22 is provided to prevent relay 10 from repicking. Without resistor 22, junction D would probably the at 0 volts, but with this resistor in the circuit, the voltage at junction D is +12 volts. Hence, relay 10 is dropped by reversing the current flow through coil 13 by temporarily driving junction B from +6 volts to approximately +18 vol-ts. As voltage increases at junction B, it will cause a slight temporary increase in voltage at A to about 6 volts. But the voltage across coil 13 will not increase sufiiciently for a long enough time in this reverse direction to repick relay 10.

When relay 10 becomes ale-energized, contact 12 will open, thus breaking the shunt path around coil 15 of relay 11. Current will now flow from source 17 through coil 15 to junction C, which is at 0 volts because coil 15 and resistor 20 are of equal resistivity. Thus, with a 12-volt potential across coil 15, relay 11 will be picked and reolose contact 14. Closure of contact 14 will have little effect on capacitor 21 since it is already charged to the input pulse voltage of 12 volts.

When the second positve pulse ends at time T5 (FIG. 2), contact 14 will be closed. Hence, capacitors 21 and 23 will concurrently discharge through their respective resistors 25, 24. Thus, the circuit will once again be in its initial state corresponding to that described as occurring at time T1. Hence, relay 11 will remain energized until relay 10 is again picked.

It may here be noted that a trigger circuit having com-.2

ponents with the parameters illustratively assumed has operated very satisfactorily in the manner above explained.

As illustrated, the coil 15 is shown wrapped around another reed relay 32 having a single pair of overlying reeds providing a normally open contact 33. The reedsof relay 32 are appropriately connected to complete any desired independent circuit whenever coil 15 is energized, which will occur concurrently with the energization of relay 11. If, as shown, one of the reeds of relay 32 is connected to source 17, an output voltage of 12 volts could be obtained at an output 34. In such event, positive voltage outputs would be obtained at outputs 30 and 34 alternatively upon successive energization of relays 10 and 32, respectively.

It should be noted, as a matter of precaution, that if the capacitance of capacitor23 is increased toward equality with that of capacitor 21, the pick time of relay 10 will be correspondingly stretched out or lengthened until eventually it will fail to pick because the difference in decay rates of the capacitors will be too small to develop the ad ditional potential necessary to pick relay 10.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A trigger circuit comprising first and second relays, means including a voltage source for supplying across the coil of said first relay a bias voltage insufiicient to pick but sutlicient to hold such relay, input means providing trigger pulses of a voltage higher than said bias voltage, first and second means for coupling the input means to opposite sides of said coil and including impedance means for delaying decay of the trigger pulse in said first means at least a predetermined time after decay of the pulse in said second means to create across said coil a voltage differential of a magnitude and duration sufiicient to energize said first relay, and an output, said first means including a normally open contact of said second relay, and the coil of said second relay and also a normally open contact of said first relay being connected in parallel to said source and output to provide an energizing voltage across the last-mentioned coil only if and while the normally open contact of said first relay is open.

2. A trigger circuit comprising first and second relays, means including a voltage source for supplying across the coil of said first relay a bias voltage insufiicient to pick but sufficient to hold such relay, an input for supplying trigger pulses, first means and second means for coupling the input to opposite sides of said coil, an output, said first means including a normally open contact of said second relay and a capacitor, said second means including a capacitor of smaller capacitance than the first-mentioned capacitor, and means providing discharge paths for the capacitors, the coil of said second relay and also a normally open contact of said first relay being connected in parallel to said source and output, whereby upon each successive pulse one of said relays will be picked and the other of said relays will be dropped.

3. The combination according to claim 1, wherein when said contact of said second relay is open and thus renders said first means ineffective, the trigger pulse will be supplied solely via said second means to the coil of said first relay for providing a reverse current through such coil sufficient to drop said first relay and open its contact, thereby to re-establish the energizing voltage across the coil of said second relay.

4. The combination according to claim 1, wherein the 0 relays are of the encapsulated reed type having only normally open contacts.

5. The combination according to claim 2, wherein said relays are of the encapsulated reed type encircled by their respective coils, and including at least one ancillary control circuit, each such ancillary circuit comprising a reed relay encircled by the coil of one or the other of said first and second relays.

6. The combination according to claim 2, including latch back means comprising a resistor connecting to the output a point in said first means intermediate said firstmentioned capacitor and the normally open contact of said second relay.

7. A circuit comprising a relay having a coil, means including a voltage source and a resistor for supplying across the coil a bias voltage insuficient to pick but sufilcient to hold such relay, input means providing pulses of a voltage higher than said bias voltage, first means including one capacitor for capacitatively coupling said input means to one end of the coil in bypass of said resistor, second means including another capacitor of lesser capacitance than said one capacitor for capacitatively coupling said input means to the other end of the coil, such that an input pulse supplied concurrently to said first means and second means will increase the voltage across the coil temporarily to a value and for a time which according to the diflYerent decay rates of said capacitors is sufficient to pick said relay so that it will be held energized by said bias voltage upon completion of such decays, and means for opening said first means to cause only said second means to be capacitatively coupled to said coil during a subsequent input pulse, thereby to cause de-energization of said relay by reverse flow of current through said coil.

References Cited in the file of this patent UNITED STATES PATENTS 2,606,234 Nijman Aug. 5, 1952 2,922,086 Stidger Jan. 19, 1960 3,042,900 Werts July 3, 1962 

1. A TRIGGER CIRCUIT COMPRISING FIRST AND SECOND RELAYS, MEANS INCLUDING A VOLTAGE SOURCE FOR SUPPLYING ACROSS THE COIL OF SAID FIRST RELAY A BIAS VOLTAGE INSUFFICIENT TO PICK BUT SUFFICIENT TO HOLD SUCH RELAY, INPUT MEANS PROVIDING TRIGGER PULSES OF A VOLTAGE HIGHER THAN SAID BIAS VOLTAGE, FIRST AND SECOND MEANS FOR COUPLING THE INPUT MEANS TO OPPOSITE SIDES OF SAID COIL AND INCLUDING IMPEDANCE MEANS FOR DELAYING DECAY OF THE TRIGGER PULSE IN SAID FIRST MEANS AT LEAST A PREDETERMINED TIME AFTER DECAY OF THE PULSE IN SAID SECOND MEANS TO CREATE ACROSS SAID COIL A VOLTAGE DIF- 